1. Field of the Invention
The present invention relates to sealing capabilities for ultra-high temperature seals, and more specifically to seals for containment of gases between gas turbine nozzles (stators) immediately downstream of a combustion chamber, and inner and outer cooling air path structures typically ahead and aft of the nozzles.
2. Description of Related Art
Seals are generally used for containment of gases between cooling path structures and the working gas flow through turbine nozzles. The turbine nozzles direct combustion gases so that the turbine blades can perform work. The turbine nozzles, however, are subject to differences in thermal expansion with adjoining components due to the heated combustion gases. The prior art seals that help achieve gas containment are generally used at temperatures lower than those targeted for the present invention, i.e., lower than 2000° F. Generally, the prior art seals consist mainly of leaf-seals and seals formed as rings in tightly convoluted nickel and nickel-cobalt alloy butt-welded strip. The formed seals are subjected to high bending stresses when accommodating engine build tolerance accumulations and cyclic thermal movements. FIG. 1 depicts a cross-section of two prior art seals, such as those described in U.S. Pat. Nos. 5,118,120 and 6,095,750.
In U.S. Pat. No. 5,118,120 issued to Drerup, et al., on Jun. 2, 1992, entitled “LEAF SEALS,” an apparatus for effecting a seal between two structural components of a turbo machine is taught, comprising a leaf seal located in the space between the two components and a spring which continuously biases the leaf seal into a sealing position against the components regardless of the pressure differential across the leaf seal.
Leaf seals are commonly employed to affect a substantially fluid-tight seal between abutting structural components in a turbo machine or other apparatus where a high-pressure area is present on one side of the structural component and a low-pressure area is present on the opposite side. FIG. 1 depicts a sectional view through a prior art turbine segment showing one nozzle blade 10 set between an inner band 11 and outer band 12 with terminating features of continuous annular components to either side. In the assembly of the majority of aircraft turbine engines today, the axis of rotation is vertical with respect to the base or first end, and the engine modules are built upward toward the second end of the engine. The view in FIG. 1 is a side view with the engine axis horizontal and its front end to the left. The seals in this figure comprise three leaf seal assemblies 13, 14 and 15, and one circular convoluted inner turbine seal ring 16.
The leaf seals of the prior art are depicted in FIG. 1. Each one is similar in construction. Leaf seal 13 is shown with an inner end 17 supported within a notch 18 formed in the vane forward outer rail 19, and an outer end 20 engageable with a combustor rear flange 22 (depicted for illustrative purposes by a triangular stop, but in actuality, a formed metal structure). Leaf seal 13 is slidably mounted on a threaded shoulder pin 24 connected and locked to the vane forward outer rail 19 by a nut 26. Leaf seal 13 is movable between a closed, sealed position, wherein its inner end 17 and outer end 20 engage the forward outer rail 19 and rear flange 22, respectively, as shown in FIG. 1, and an open position in which at least one of the ends 17, 20 of the leaf seal disengage a structural component. A biasing means 27, usually in the form of a spring, is mounted to one of the structural components and engages the leaf seal at a point intermediate the portions of the leaf seal that contact the structural components. The spring is effective to force the leaf seal against each structural component so as to maintain the leaf seal in a closed, sealed position.
In U.S. Pat. No. 6,095,750 issued to Ross, et al., on Aug. 1, 2000, entitled “TURBINE NOZZLE ASSEMBLY,” a nozzle assembly is taught in which an outer band, an inner band, and at least two vanes disposed between the outer and inner bands are fabricated as a nozzle segment. As shown in FIG. 1, the arrangement for mounting the circular convoluted inner turbine seal ring 16 to the inner nozzle support 32 is depicted in more detail. The inner nozzle support 32 has at its axially and radially distal end, an annular radially outwardly extending aft mounting flange 34. An annularly radially outwardly extending forward mounting flange 36 is formed on the inner nozzle support 32, so as to form a gap with aft mounting flange 34. A retention flange 38 formed on the inner band 40 of the nozzle segment is disposed between the aft and forward mounting flanges. The inner nozzle support 32 positions the nozzle segment axially by virtue of the flow of combustion gases pressing the retention flange 38 against the aft mounting flange 34. The forward mounting flange 36 is provided to prevent forward movement of the nozzle segment in the unusual event of an engine stall.
These seals are known to be prone to distortion when used in connection with segmented nozzles having slightly varying heights. Even when new, leaf seals exhibit unwanted leakage, causing as much as a two (2) percent increase in fuel consumption compared to the initial performance of engines fitted with formed seal rings, which in some applications proved to have limited life due to failure by disintegration.
Furthermore, these prior art seals are generally produced in formable alloys and have been shown to be prone to stress relaxation at their maximum operating temperatures.